The present invention relates generally to optical data storage. More specifically, writing high-density multi-level or binary data to an optical disk made of material whose state may be changed upon radiation by a laser beam is disclosed. A region of material is modified using a laser and the controlled formation of the material state and its distribution within the region is described.
Information may be stored on an optical disc by creating regions or xe2x80x9cmarksxe2x80x9d having a different reflectivity than the surrounding surface of the disc. In an optical phase change disc, such regions are formed by irradiating the surface of the disc with a writing laser that causes a region to be warmed and melted or partially melted. As the region cools, the region may change to a crystalline or amorphous state or some combination of crystalline and amorphous states. When a reading laser is incident on such a region, the reflected light can be measured and the state of the region can be determined. The state of the region represents stored data. Different levels of reflectivity may represent different data levels.
FIG. 1A is a cross section of a typical optical phase change disc 100. Optical phase change disc 100 includes a substrate 102. A first dielectric layer 104 is deposited on the substrate. A recording layer 106, which is composed of a phase change material, is deposited on top of dielectric layer 104. A second dielectric layer 108 is deposited over recording layer 106. A reflective layer 110 is deposited over dielectric layer 108. Finally, a protective resin layer 112 is deposited over reflective layer 100. The layers described above are provided as an example only and that the techniques described herein are applicable to other types of phase change discs as well as other optical discs that utilize different recording mechanisms. U.S. Pat. Nos. 5,136,573 and 5,144,615, (the ""573 and ""615 patents, respectively) issued to Kobayashi, which are herein incorporated by reference for all purposes, describe techniques for multilevel recording using optical phase change discs. Kobayashi describes lowering the reflectivity of an initially amorphous region by forming crystalline material and that more crystalline material may be formed as the writing laser power is increased. Kobayashi also discloses an overwrite technique that forms a crystalline region using a low level biasing energy and increases the reflectivity by forming a crystalline region at certain spots using energy pulses that create amorphous regions.
FIG. 1B illustrates the biasing signal disclosed in the Kobayashi patent as well as the different pulse signal levels for creating different amounts of amorphous material. Kobayashi mentions that either power or pulse width may be used to vary the amount of laser energy deposited on a region, but does not disclose a specific scheme for varying pulse width. FIG. 1C illustrates the claimed results with reflectivity increasing as the amount of amorphous material formed increases.
Kobayashi discloses different types of written spots. In the ""573 patent, a record spot that is smaller than the size of a reading laser beam is disclosed that increases in size as the energy deposited by the writing laser increases. FIG. 1D illustrates the varying size of the written region. In the ""615 patent, varying length spots that encode information with both their lengths and varying levels of reflectivity that result from different degrees of crystallization are disclosed. FIG. 1E illustrates different length marks having different reflectivities.
Kobayashi does not describe a technique for handling spots that are close enough to each other that writing one spot affects the writing of other spots. In order to further increase the density of recorded marks on phase change discs, it would be desirable to develop techniques for placing variable reflectivity marks closer together. Furthermore, it would be useful if more reliable techniques could be developed for varying the reflectivity of a region. A more reliable overwrite process for phase change discs is also needed.
Conventional thinking is that the minimum size of recorded data marks in optical systems (including systems that use a phase change media or other optical recording media) is limited to the size of the reading laser beam and the writing laser beam. While optical techniques have been developed for reducing the laser beam size of both reading and writing lasers, it would be useful if even smaller marks could be made on the disc so that the density of information stored on the disc could be increased.
A method of writing marks on a phase change material is described. Marks are written in a manner such that their size can be less than the size of the focused spot of a writing laser. By forming marks smaller than the reading laser beam, the reflectivity of a region of material can be varied with great precision. The reflectivity of a region is controlled by varying the relative amount of material in crystalline and amorphous phases. The total amount of crystalline and amorphous material in a region is controlled by creating marks of various sizes or shapes. The mark size and shape is controlled by placing the leading and trailing edges of laser pulses such that the timing of a second laser pulse further modifies the region of material irradiated by a first pulse. Additional modification of the mark size and shape results from controlling the time course of the laser power during the pulse. Existing marks may be directly overwritten by irradiating previously recorded regions with the methods described below.
In one embodiment, a method of recording information on an optical disc is disclosed. The method includes irradiating a region of the optical disc with a first dose of laser energy. A first portion of the region is irradiated with a second dose of laser energy in a manner that causes the first portion of the region irradiated with the second dose of laser energy to be in a different state than a second portion of the region that is not irradiated by the second dose of laser energy.
In another embodiment, a write strategy processor is configured to generate control signals for writing data to an optical disc comprising a processor configured to specify a first laser pulse for irradiating a region of the optical disc with a first dose of laser energy and a second laser pulse for irradiating a first portion of the region with a second dose of laser energy in a manner that causes the first portion of the region irradiated with the second dose of laser energy to be in a different state than a second portion of the region that is not irradiated by the second dose of laser energy.
In another embodiment, a method of recording information on an optical disc includes heating a region of the optical disc with a first dose of laser energy. A first portion of the region is heated with a second dose of laser energy in a manner that causes the first portion of the region irradiated with the second dose of laser energy to be in a different state than a second portion of the region that is not heated by the second dose of laser energy.
In another embodiment, a method of recording data on a phase change optical disc includes melting a region of phase change material and directing energy to a first portion of the region so that the first portion of the region becomes crystalline. The size of the first portion determines the data written to the region.
In another embodiment, a method of recording data on a phase change optical disc includes causing an amorphous mark to be formed within a region of the optical disc wherein the size of the amorphous mark within the region determines the data stored in the region.
In another embodiment, a method of recording data on a phase change optical disc includes irradiating a region of the optical disc with a first pulse of laser energy having a first pulse rising edge and a first pulse falling edge and irradiating a first portion of the region with a second pulse of laser energy having a second pulse rising edge and a second pulse falling edge. The first pulse falling edge causes a transition from crystalline material to amorphous material and the second pulse rising edge causes a transition from amorphous material to crystalline material.
In another embodiment, a method of recording data on a phase change optical disc includes irradiating a region of the optical disc with a first laser beam having a first central intense beam portion and a first less intense annular beam portion and irradiating a first portion of the region with a second laser beam having a second central intense beam portion and a second less intense annular beam portion. The first less intense annular beam portion defines a first amorphous mark boundary and the second less intense annular beam portion defines a second amorphous mark boundary.
In another embodiment, a write strategy processor is configured to generate control signals for writing data to an optical disc. The write strategy processor includes processor configured to specify a first pulse of laser energy having a first pulse rising edge and a first pulse falling edge and a second pulse of laser energy having a second pulse rising edge and a second pulse falling edge. The first pulse falling edge causes a transition from crystalline material to amorphous material and the second pulse rising edge causes a transition from amorphous material to crystalline material.
In another embodiment, a method of recording data on an optical disc includes writing marks having a leading edge and a trailing edge wherein the leading and trailing edges of the marks are determined by different pulses of a writing laser and wherein the marks are smaller than the beam size of the writing laser.
In another embodiment, a method of recording data on a phase change optical disc having a layer of optical phase change material includes irradiating a region of the disc with a central intense beam portion that melts the optical phase change material and irradiating the region with a less intense annular beam portion that slows cooling of the region so that the melted optical phase change material is converted to a crystalline state.
In another embodiment, a method of writing an amorphous mark on a phase change optical disc includes irradiating a first region on the phase change optical disc with a first dose of energy. The first dose of energy is sufficient to substantially melt the first region on the phase change optical disc. A second region of the phase change optical disc is irradiated with a second dose of energy. The second dose of energy is sufficient to slow the cooling of a portion of the first region of the phase change optical disc so that the portion of the first region becomes crystalline.
In another embodiment, a method of storing information on an optical disc includes determining a data level to be stored in a region of an optical disc. The data level is one of a set of possible data levels that includes more than 2 levels.
A region of the optical disc is melted with a laser beam and thermal energy is delivered to a first portion of the region so that the first portion of the region cools more slowly than the remainder of the region. The size of the first portion is selected to correspond to the determined data level.
In another embodiment, a method of storing information on an optical disc includes forming a crescent shaped mark. The size of the crescent shaped mark represents a level of data selected from a set of possible data levels having more than two possible data levels.
In another embodiment, a method of writing a multilevel mark on an optical disc having a layer of phase change material includes irradiating a region of the optical disc with radiation that is at least sufficient to melt the phase change material. The energy of the radiation is modulated according to a multilevel data signal that is to be stored in first region in a manner such that as the energy of the radiation is increased, the melted phase change material tends to form an increasingly large crystalline region.
In another embodiment, a method of writing a multilevel mark on an optical disc having a layer of phase change material includes generating a first energy pulse at a first time. The first energy pulse width is modulated according to a first multilevel data value that is to be stored. A second energy pulse is generated at a second time. The second time is a fixed time interval after the first time. The second energy pulse has a pulse width and a power wherein the pulse width is modulated according to a second multilevel data value that is to be stored.
In another embodiment, a method of writing a multilevel mark on an optical disc having a layer of phase change material includes generating a series of pulses. Each pulse has a rising edge and a trailing edge. Each rising edge occurs periodically and each rising edge causes an amorphous to crystalline transition on a phase change optical disc. Each trailing edge causes a crystalline to amorphous transition on a phase change optical disc so that each amorphous to crystalline transition occurs periodically.
In another embodiment, a method of writing a multilevel mark on an optical disc having a layer of phase change material includes generating a series of pulses. Each pulse has a rising edge and a trailing edge and each rising edge causes an amorphous to crystalline transition on a phase change optical disc. Each trailing edge causes a crystalline to amorphous transition on a phase change optical disc. The centers of each pulse occur periodically so that amorphous regions are formed having centers that occur periodically.
In another embodiment, a method of writing a multilevel mark on an optical disc having a layer of phase change material includes generating a first energy pulse during a first time interval. The first energy pulse has a pulse width and a power. The pulse width is modulated according to a first multilevel data value that is to be stored and the first energy pulse is centered in the first time interval. A second energy pulse is generated during a second time interval. The second energy pulse has a pulse width and a power and the pulse width is modulated according to a second multilevel data value that is to be stored and wherein the second energy pulse is centered in the second time interval.
In another embodiment, a method of recording information on a medium includes activating a recording head that interacts with an active zone of a recording medium in a manner such that a first portion of the active zone has a first property and a second portion of the active zone has a second property. The recording head is deactivated so that a first transition between the first property and the second property is created. The recording head is moved and then reactivated so that a second transition between the second property and the first property is created.
In another embodiment, a method of recording information on a phase change material includes irradiating a region of the phase change material so that at least a portion of the irradiated region is melted and controlling the final phase of the irradiated region by controlling its subsequent temperature profile by modulating the power of a laser beam.
In another embodiment, a method of recording information of a phase change material includes melting a region of the material and causing a first portion of the melted region to cool slowly and become crystalline. A second portion of the melted region cools rapidly and become amorphous. The relative sizes of the crystalline and amorphous regions determine the data written to the region.
These and other features and advantages of the present invention will be presented in more detail in the following detailed description and the accompanying figures which illustrate by way of example the principles of the invention.